Pore evolution characteristics and porosity calculation of ultra-low permeability reservoirs

Through integrated application of core,electron microscope,the casting thin sections,cathodoluminescence,etc,the research on reservoir sedimentation and diagenesis characteristics of Chang-6 member of Wucangpu oil area in Ordos basin has been carried out.The results indicate the rocks are of low compositional maturity and high content of volatile components.The main factors for poor reservoir properties in the research area are sedimentary micro-facies,such as bar microfacies and underwater distributary channel microfacies,and the strong diagenesis in late periods.According to the characteristics of porosity evolution,corresponding porosity calculation model has been established.The results showed that the original porosity of the reservoir average is38.6%.Due to strong compaction and cementation,pore loss was serious,and the average porosity loss was 27.2%.Dissolution and metasomatism increased the pore space;the average increased porosity was 3.2%.Through diagenesis process,the average porosity at present is 8.2%.